The United States Government is committed to removing obsolete and aged munition and explosive inventories from the active arsenal. Historically, demilitarization programs focused on disposal or destruction. Recently, there have been efforts to develop recycling and/or reclamation processes that permit explosives and higher valued constituents of munition systems to be recovered and re-used in either military or civilian applications.
There are significant stockpiles of octols (mixture of TNT and HMX), cyclotols such as Composition B (mixture of TNT and RDX) as well as other explosive mixtures containing TNT that are no longer part of the active inventory and are awaiting demilitarization. These explosives currently exist as either bulk materials or they are contained in munitions.
The recovery of the individual explosive components contained in mixtures of nitramines and TNT can be highly desirable in demilitarization scenarios in which the mixture no longer has military or commercial value. To date, there has been little published art relating to the recovery of these constituents using solvent extraction. U.S. Pat. No. 5,977,345 to Spencer discloses a method in which the TNT component is melted and separated from the nitramine component by use of a sieve tray. The solid nitramine is then contacted with a solvent that preferentially dissolves the TNT leaving the nitramine in a relatively high purity state.
Both RDX (cyclotrimethylenetrinitramine) and HMX (cyclotetramethylene tetranitramine) have a significant solubility in molten TNT resulting in both a yield loss of these constituents as well as in contaminating the recovered TNT.
The Spencer method, with regard to demilitarizing munition-derived materials and recovering the RDX component, results in both yield and purity issues with respect to the recovered solid nitramine and TNT. The explosive mixture derived from munitions will usually contain additional materials associated with the liner (typically an asphalt-based compound) and the sealing material (typically, a resin or rosin based material). It has been shown that the presence of trace quantities of asphalt enhance the sensitivity of TNT as measured by conventional impact and thermal sensitivity tests. The contacting of molten TNT and asphalt while passing through a sieve device raises safety issues that must be addressed when considering a commercially sized (>100 lb/day) process system. Additionally a de-sensitizing agent is often used with the nitramine component. For example in Composition B mixtures, a natural wax is employed to coat the RDX particles in order to reduce the sensitivity of this material with respect to mechanical shocks. Other types of de-sensitizing agents include soaps and stearates. The deposition of the de-sensitizing agent is an important aspect of the recovery process possibly requiring an additional step for separation and removal from the recovered energetic materials.
The munition liner and sealing materials will typically collect on the sieve along with the nitramine. The asphalt material may transform to a highly viscous paste-like material that can readily block the sieve. The presence of these additional components within the solid nitramine matrix can adversely affect the purity and subsequent re-use as a high valued material. In addition, the asphalt liner material is highly soluble in toluene (a solvent for TNT) and can thus contaminate the recovered TNT. Spencer teaches the use of toluene as the solvent for removing residual TNT from RDX.
Therefore, there remains a need in the art for an improved method for recovering TNT and nitramines from mixtures containing same, particularly munitions containing same.